This invention relates generally to conserving bandwidth in videotelephony systems, and more specifically to conserving bandwidth in videotelephony systems by using digital zooming and picture-in-picture functionality.
Videotelephony provides symmetric audio and video streaming for an image source across a communications network. The video stream may be compressed using a variety of compression/transmission standards, including: MPEG-4, H.323, H.261 and H.263. These compression standards provide for some conservation of bandwidth, but since videotelephony relies on telephony links that can be limited to 56 Kbs or lower (e.g., cellular) the bandwidth for videotelephony may remain severely constrained in some instances. Constrained bandwidth causes image quality to suffer, often preventing viewers from detecting important visual queues from images displayed in the videotelephony system.
The ability to zoom the image on a videotelephony display can increase the viewer's ability to see detail, but at the cost of requiring a re-transmission of the newly zoomed image. This re-transmission consumes bandwidth, thereby reducing the available refresh frequency, and thus reducing the quality of the image displayed.
Images in videotelephony systems can be captured using standard pan-tilt-zoom cameras having optical and/or digital zooming capabilities. Once captured, images in videotelephony systems are digitally transmitted from the far-end (i.e., camera-end) to the near-end (i.e., display-end). Certain videotelephony display systems implement picture-in-picture technology, this is often used to view the near-end image as it is being seen by the far-end display of the videotelephony link and visa versa. Using picture-in-picture technology a viewer can track how they are being seen. Re-transmissions based upon re-aiming and re-zooming the cameras in a videotelephony system consume a significant amount of videotelephony bandwidth.
Intel Corporation of Santa Clara, Calif., USA provides videotelephony capabilities through its ProShare® Video Conferencing Systems. PictureTel Corporation of Andover, Mass., USA has developed the PictureTel 900 Series Collaboration System for video conferencing. Polycom of Milpitas, Calif., USA provides video conferencing solutions for personal, conference room and board room use. Ezenia! Inc. of Burlington, Mass., USA provides video conferencing through its Encounter family of products. These existing systems provide limited zooming and some picture-in-picture functionality, but none conserve bandwidth by providing digital zooming in a videotelephony system using near-end picture-in-picture functionality.
Video screen magnifiers exist to digitally zoom portions of video display (e.g., computer) screens. The Microsoft Magnifier Version 1.0 (Windows 98 Operating System) provides zooming by splitting the screen and displaying a magnified (zoomed) version of the portion of the screen having mouse cursor or keyboard focus. The desired effect is to have the mouse cursor act as a magnifying glass as it moves over portions of the screen. Alternate versions of screen magnifiers have been developed, for example The Bigshot Magnifier (www.bigshotmagnifier.com) will zoom the full display screen or the active window on the display screen. The Screen Loupe Magnification Utility (www.gregorybraun.com) provides a separate floating window that magnifies a viewer defined area under the mouse cursor. These screen magnifiers provide some rudimentary screen zooming, but are not integrated into a videotelephony system, lower screen resolution and do not conserve bandwidth by providing digital zooming in a videotelephony system using picture-in-picture functionality.